Dart Queue
last modified April 4, 2025
In Dart, Queue is a collection that implements a double-ended queue. It allows efficient addition and removal at both ends. Queue follows FIFO (First-In First-Out) principle by default.
Queue is part of dart:collection library. It provides more functionality than List for queue operations. Unlike List, Queue doesn't implement index-based access.
Creating a Queue
The simplest way to create a Queue is using the Queue constructor.
import 'dart:collection';
void main() {
var queue = Queue<String>();
queue.add('Apple');
queue.add('Banana');
queue.add('Cherry');
print(queue);
}
We create a Queue of Strings and add three elements. The add method appends elements to the end of the queue. The generic type specifies the element type.
$ dart main.dart
{Apple, Banana, Cherry}
Adding Elements to Queue
Queue provides multiple methods for adding elements at both ends.
import 'dart:collection';
void main() {
var queue = Queue<int>();
// Add to end
queue.add(1);
queue.addLast(2);
// Add to beginning
queue.addFirst(0);
// Add multiple
queue.addAll([3, 4]);
print(queue);
}
We demonstrate various addition methods. add and addLast append to the end, while addFirst prepends to the start. addAll adds multiple elements at once.
$ dart main.dart
{0, 1, 2, 3, 4}
Removing Elements from Queue
Queue provides methods to remove elements from both ends efficiently.
import 'dart:collection';
void main() {
var queue = Queue.from([10, 20, 30, 40, 50]);
// Remove from start
var first = queue.removeFirst();
// Remove from end
var last = queue.removeLast();
// Remove specific element
queue.remove(30);
print('Removed: $first, $last');
print('Remaining: $queue');
}
removeFirst and removeLast efficiently remove from ends. remove deletes the first occurrence of a value. All these methods modify the queue in-place.
$ dart main.dart
Removed: 10, 50
Remaining: {20, 40}
Queue Operations
Queue provides various operations for inspection and modification.
import 'dart:collection';
void main() {
var queue = Queue.from(['Red', 'Green', 'Blue']);
// Check properties
print('First: ${queue.first}');
print('Last: ${queue.last}');
print('Length: ${queue.length}');
print('Is empty: ${queue.isEmpty}');
// Clear queue
queue.clear();
print('After clear: $queue');
}
We demonstrate common Queue operations. first and last peek at elements without removing. length and isEmpty check size. clear removes all elements.
$ dart main.dart
First: Red
Last: Blue
Length: 3
Is empty: false
After clear: {}
Iterating Over Queue
Queue can be iterated using standard iteration methods.
import 'dart:collection';
void main() {
var queue = Queue.from([1, 2, 3, 4, 5]);
// For-in loop
print('For-in:');
for (var num in queue) {
print(num);
}
// forEach
print('\nforEach:');
queue.forEach(print);
// Iterator
print('\nIterator:');
var it = queue.iterator;
while (it.moveNext()) {
print(it.current);
}
}
We show three ways to iterate a Queue. The for-in loop is most common. forEach provides a functional approach. Iterator offers manual control.
$ dart main.dart For-in: 1 2 3 4 5 forEach: 1 2 3 4 5 Iterator: 1 2 3 4 5
Best Practices
- FIFO Operations: Use Queue when you need efficient FIFO operations.
- No Index Access: Avoid Queue if you need random access by index.
- Memory Efficiency: Queue is more memory efficient than List for queue operations.
- Type Safety: Always specify generic type for type safety.
Source
This tutorial covered Dart's Queue interface with practical examples demonstrating its key features and usage patterns.
Author
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